Wednesday, October 23, 2013

QM silent on free will, whether complete or not

While I think most of us reject the notion of contracausal free will (although many of us accept other forms of “free will”), Eric refuses to do so. Because we don’t fully understand physics, he sees the acceptance of determinism as unscientific — indeed, metaphysical:

There is not a shred of evidence for the claim that physics is complete, so that we can simply say that the whole of reality is tied up in a causal nexus such that all our “actions” are determined. Indeed, as John Dupré points out in his book Human Nature and the Limits of Science, science, and therefore, empirical demonstration, only works on very carefully isolated phenomena, where the effects of each underlying particle or force are known, and all extraneous (and therefore incalculable) causes are excluded. Science works by means of models and abstraction, and does not provide a unified theory of reality.

But physics does not have to be complete for us to accept determinism on a macro level. Although I don’t know many physicists, the two I’ve spoken to about this at length (Sean Carroll and Steve Weinberg) agree that we know enough about the physics of “everyday life” to provisionally accept that human behavior is indeed determined by the laws of physics. Even if quantum mechanics produces some fundamental unpredictability in our neurons and hence in our behavior, that gives no leeway for “free choice”. Such choice would be equivalent to tossing a coin, and nobody wants to think of free will as anything like that.

Just addressing the physics (and avoiding the religion and poetry issues), Coyne has some big misunderstandings of quantum mechanics.

Sure, I provisionally accept that human behavior is indeed determined by the laws of physics. In spite of claims by Weinberg and others, there is no evidence that physics is complete, whatever that means.

When it comes to free will, quantum mechanics is remarkably neutral on the subject. A century ago, a scientist probably would have said that a hypothetically complete theory of physics must necessarily prohibit free will, or maybe explicitly allow it somehow. But quantum mechanics does neither. Quantum mechanics seems almost designed to make it impossible to draw conclusions about free will.

Even so, the standard model is clearly not the final theory. Its equations involve a score of numbers, like the masses of quarks, that have to be taken from experiment without our understanding why they are what they are. If the standard model were the whole story, it would require neutrinos to have zero mass, while in fact their masses are merely very small, less than a millionth the mass of an electron. Further, the standard model does not include the longest-known and most familiar force, the force of gravitation. We commonly describe gravitation using a field theory, the general theory of relativity, but this is not a quantum field theory in which infinities cancel as they do in the standard model.

He has been saying for decades that there is something wrong with the standard model. He even wrote a book about it. But the evidence from the LHC has overwhelmingly confirmed the standard model, and proved everyone else wrong. So far, anyway.

I don't see how physics can be both "complete" and "clearly not the final theory." And even if human behavior is determined by the laws of physics, those laws are not even deterministic, so they do not imply that human behavior is determined.

Coyne's coin toss argument is strangest of all. If physicists say that they cannot predict a nuclear decay or some other phenomenon, they say it is like a coin toss. So maybe a human free choice is like a coin toss in that sense. But Coyne says "nobody wants to think of free will as" like a coin toss. Yes, they do. Free will is like a coin toss in that it cannot be externally predicted. That is exactly how everyone wants to think about free will.